Beverages are commonly packaged in containers which are made from translucent materials. Examples of such materials include glass and plastic. Because they are formed of translucent materials, such containers do not completely block light from passing through the container wall. Accordingly, the contents of a translucent container may be exposed to light from outside of the container.
The taste of some beverages may be detrimentally affected by light. In beer, for example, exposure to light causes a breakdown of certain sulfur compounds existing in the beer. The presence of these sulfur compounds is due to the addition of hops, an ingredient of beer. The products of this breakdown result in an undesirable flavor profile in the beer which is detectable by both taste and smell. This flavor profile is commonly referred to in the beer brewing industry as "light-struck flavor" and is often described as having a "skunky" flavor and odor.
It has been found that some wavelengths of light, more than others, induce light struck flavor in beer. FIG. 1 graphically illustrates the amount of light struck flavor induced in beer versus light wavelength. As can be seen, wavelengths of light of up to about 550 nm have the greatest impact on light struck flavor in beer. Wavelengths of light above about 550 nm, on the other hand, have little effect.
Because of the light-struck flavor problem, it is desirable to reduce or eliminate the exposure of beer to light in the wavelength range described above. This represents a particular challenge when beer is packaged in translucent containers. The ability of a translucent material to block the transmission of light depends upon both the thickness and the color of the material used. The most common translucent containers used for packaging beer are glass bottles.
The manufacture of glass bottles begins with the preparation of raw materials. A batch of raw materials is formed by measuring sand, soda ash and other ingredients in precise quantities and then mixing them together. The batch is then conveyed to storage silos located over large melting furnaces. The mixed batch materials are continuously metered into furnaces to replace molten glass which is dispensed from the furnaces after melting.
The furnaces are heated by a combination of natural gas and electricity and are operated at a temperature of over 2500 degrees Fahrenheit. The melted mixture of raw materials forms molten glass which flows from the furnaces through refractory channels, also known as forehearths, to a position over bottle forming machines.
A bottle forming machine known in the industry as an "I.S. machine" draws the glass into individual gobs and drops each gob into a blank mold. The blank mold forms a bottle preform, also referred to as a parison. The preform is transferred to a blow mold where it is blown by compressed air into a bottle.
An I.S. machine typically has between six and sixteen individual sections, with each section having from one to four blow mold cavities. Each section may be capable of manufacturing one to four bottles at a time. A typical eight section, triple gob, I.S. machine used in the production of beer bottles may produce 270 beer bottles per minute.
After the bottles have been blown, they are transferred from the respective blow mold cavities onto a moving conveyor belt. The finished bottles transferred onto the conveyor from the blow mold are still red hot (approximately 1,000 degrees Fahrenheit). These hot bottles are conveyed by the conveyor belt through a hot end coating hood where they are chemically treated with a stannous chloride compound for strengthening.
After passing through the hot end coating hood, the hot bottles are conveyed through an annealing oven or lehr where they are reheated and then cooled in a controlled manner to eliminate stresses in the glass. The annealing process is the last process which takes place at the hot end of the production line. The portion of the production line downstream from the annealing oven is referred to as the "cold end" of the production line. At the cold end of the production line, bottles are conveyed through a series of inspection devices.
After passing through the cold end inspection stations, bottles are transferred to a case packer machine, placed into a cardboard carton and conveyed to a palletizer machine for being placed in pallets. Loaded pallets are then shipped to a filling facility, such as a brewery.
In order to provide effective light-blocking properties in glass containers, such as glass bottles, amber colored glass is generally used to form the bottles. When making amber colored glass bottles, iron-bearing minerals such as pyrite or melite and graphite are generally added to the batch in precise quantities. The color of the finished glass depends upon the specific chemistry of the glass batch which can itself vary due to, e.g., variations in the raw material used. Often, previously manufactured glass bottles are crushed and added to the batch. Because crushed glass, commonly referred to in the industry as "cullet", varies in composition, its addition also causes variations in the feed stock for the glass and may, thus, impact the color and quality of the final glass produced.
Accordingly, it is desirable to regularly perform quality control checks on glass bottles to ensure that they are capable of adequately blocking light. Normally, to accomplish such checks, samples of bottles are removed from the glass production line for testing. One object of this testing is to detect glass batch material variations which allow an unacceptable amount of light to be transmitted through the bottle. Another object of such testing is to test new bottle designs which may have different wall thicknesses than previously used designs.
One such test that is commonly performed is a flavor panel test. In this type of test, bottle samples are first filled with beer. The bottles are then exposed to a predetermined level of light for an extended time period. This time period may be, for example, 14 days or longer.
After exposure to light for the requisite time period, the beer in the bottles is tasted by members of a trained beer tasting panel. The panel members then determine if any light struck flavor exists in the beer, and the bottles are then accepted or rejected as appropriate.
One problem with the flavor panel test is the relatively large amount of time which elapses between bottle manufacture and the results of the test. During the several day period required for the test, tens of thousands of bottles may be produced. Accordingly, if a problem is detected by the flavor panel test, all of bottles produced during the testing period may have to be destroyed. This time delay may represent a particular problem when a new bottle design is being introduced.
Because of this time delay problem, efforts have been made to analyze bottle samples shortly after they are produced to predict whether the bottles will pass the flavor panel test. The traditional method used to accomplish this analysis is a destructive test in which a portion is first cut out of the bottle wall. This portion may measure approximately 1 cm by 5 cm and may be cut from the label panel portion of the bottle. The cut portion is then placed into a spectrometer and the transmittance of light through the portion is then measured at a particular wavelength of light. Typically, the thickness of the cut portion is also measured and the measured transmittance is then standardized back to a standard glass thickness, e.g., 1/8 inch thick glass. As can be appreciated, this procedure focuses only on the color density of the glass, and not its overall ability to block light transmittance.
If the procedure indicates that the glass is defective, then changes can immediately be made to the process or bottle design, or both, to correct the problem and the time delay associated with the flavor panel test can be avoided. If, on the other hand, the procedure indicates that the glass is acceptable, then the production of glass bottles can continue with the expectation that the flavor panel test will also be favorable.
The destructive test described above is intended to solve the time-delay problem associated with the flavor panel test. In reality, however, it has been found that the destructive test often fails to accurately detect defective bottles which are subsequently rejected by the flavor panel test. In other words, the flavor panel test often rejects samples of particular glass batches or bottle designs that had previously been indicated as acceptable by the destructive test.
Such failures by the destructive test often occur because, as described above, only color density is analyzed and because light of only a single wavelength is measured. The traditional destructive test measures light transmittance only at around 550 nm. As previously described, however, light struck flavor in beer is induced by a range of light wavelengths of up to about 550 rim.
FIG. 2 graphically illustrates an example of glass which is well suited for preventing light struck flavor in beer. As can be appreciated, the glass illustrated in FIG. 2 allows the passage of very little light in the light struck flavor wavelength range of less than 550 nm.
FIG. 3 graphically illustrates a glass sample which exhibits relatively low, e.g., about 3%, transmittance at 550 nm, but which exhibits relatively high transmittance over the majority of the light-struck flavor inducing range. Glass exhibiting these characteristics might pass the destructive test, previously described, because the destructive test only analyzes light transmittance at 550 nm. Since a large amount of light in the light-struck flavor inducing range is unblocked by the glass, however, light struck flavor might very well be induced and a bottle made from such glass would, therefore, most likely fail the flavor panel test.
In addition to the problem described above, the destructive test also has the disadvantage of being slow. A typical test using the destructive testing method outlined above, may take approximately two hours.
Because the destructive test entails cutting portions out of bottles, it requires manual labor and, accordingly, is not conducive to automation. Finally, the destructive test, as its name indicates, requires destruction of the bottle being tested. Accordingly, bottles tested by this method cannot later be used for packaging beer or other beverages.
Thus, it would be generally desirable to provide an apparatus and method which overcomes these problems associated with the testing of beverage containers for light transmittance.